The invention comprises three different but related types of electrochemical cell.
The three electrochemical cells of the invention share several important common features.
In the first instance, they are all portable. That is, they can each be used in the field, e.g. outside the laboratory. They can be moved to any desired location to make electrochemical measurements on a wide variety of different sized and shaped substrates. Obviously, even though the electrochemical cells of the invention are designed to be usable outside the laboratory, they will work just as well in the laboratory, if desired.
Secondly, each electrochemical cell has the ability to be removably and nondestructively secured to one surface of a substrate of indefinite size. This feature derives from the attachment means used with each electrochemical cell of the invention. Removable and nondestructive attachment is defined herein to mean that the electrochemical cells of the invention may be attached and then easily removed from the substrate with no damage at all to the electrochemical cell and with only minimal damage to the substrate. For example, the substrate may require a small amount of cleaning because of spilled electrolyte. In addition, certain types of electrochemical measurements may require any coating of the substrate to be removed prior to taking the measurements. Obviously, this coating would have to be replaced in order to return the substrate to its original condition.
The attachment means permits the cells to be used to make electrochemical measurements on substrates of widely varying sizes and shapes. Since the attachment means will secure the electrochemical cells of the invention to substrates of widely varying sizes, in-situ electrochemical measurements may be made on portions of existing structures which may be quite large—for example ships, bridges, or buildings.
Prior art electrochemical cells typically are limited to making measurements on relatively small sized substrates, capable of being inserted into the cell interior. Some prior art cells have the ability to make measurements on larger substrates but require access to an edge of the substrate. Thus, most all of the prior art electrochemical cells are severely limited as to the size of the substrates they can work with.
Lastly, they are all relatively compact and rugged compared to existing electrochemical cells. For example, glass is often used in the construction of the prior art electrochemical cells and, for obvious reasons, a glass electrochemical cell can not fairly be characterized as being “rugged”. The electrochemical cells of the invention are made primarily of modern polymeric materials which are much more rugged than glass.
The first and most basic electrochemical cell comprises an analytical chamber which can be utilized with existing prior art potentiostats. This chamber has means to contain the necessary electrolyte and means to secure a counter electrode and a reference electrode therein. The chamber also has an adjustable attachment means to permit the chamber to be removably and nondestructively attached to and then removed from the surface of a substrate of indefinite size.
The second electrochemical cell is a compact, rugged self-contained portable probe comprising an electrochemical cell and potentiostat to perform electrochemical measurements. The probe of the invention is particularly useful to monitor corrosion on bare and coated substrates. The probe of the invention is designed to work on metals and other conductive substrates. It is also designed to determine the effectiveness or integrity of conductive and nonconductive coatings on conductive substrates.
The third electrochemical cell is a modification of the second cell which retains the self-contained electronics component of the second electrochemical cell, but eliminates the fluidics handling portion of the second embodiment.
Corrosion is a wide-spread problem that affects nearly all industry and government sectors. A recent report determined that the direct cost of corrosion in the United States to be 3.1% of the Gross Domestic product (GDP) [G. H. Koch, et al. “Corrosion Costs and Preventive Strategies in the United States,” Report by CC Technologies Laboratories, Inc. to Federal Highway Administration (FHWA), Office of Infrastructure Research and Development, Report FHWA-RD-01-156, September 2001]. This corresponds to $300B annually or $1000 per person. This figure includes only the direct costs (e.g., corrosion prevention, corrosion inspection, and replacement or refurbishment of corroded structures). The indirect costs (e.g., lost productivity, taxes, and overhead) were conservatively estimated to be equal to the direct costs.
Thus, there is a pressing need to determine or monitor the susceptibility or rate of corrosion of critical structures and components in the field. Because corrosion is an electrochemical process, electrochemical measurements are the most effective means to determine if a material is corroding, is susceptible to corrosion, or is protected from corrosion. These measurements are generally acquired by placing the material being studied (the working electrode) in a liquid electrolyte along with reference and counter electrodes to form an electrochemical cell and using a potentiostat (a controlled power supply with a sensitive zero-resistance ammeter (ZRA) or other galvanometer) to apply a potential or voltage between the reference electrode and the material being studied and measuring the current induced between the material and the counter electrode. The potential can be constant or varying and it and the current can be either DC or AC. The relationship of the current to the potential or the impedance (potential divided by current for ac measurements) allows one skilled in the art to determine whether the material is corroding, susceptible to corrosion or protected from corrosion and if a coating is protective or not. The potentiostats are generally relatively large and heavy bench instruments that require standard electrical power. An example of a prior art potentiostat would be the Gamry Reference 3000 potentiostat that is approximately 20-cm×23-cm×30-cm and weighs approximately 6 kg.
In the procedure described above, the material or specimen must be relatively small with dimensions in inches or centimeters to allow the specimen to be immersed in a beaker or other container filled with a suitable electrolyte. For larger specimens or structures that are too large to immerse completely in an electrolyte, electrochemical measurements can sometimes be acquired if the desired area of the structure is horizontal or nearly horizontal by placing a bottomless cylinder (or similar construction) on the structure and sealing it to the structure with an o-ring, gasket, sealant, or other means so that the structure becomes the bottom of the container. Other configurations allow the material to be vertical and form the side of a horizontal cylinder with openings along the top of the cylinder to allow the electrolyte and electrodes to be added. The container is then filled with the appropriate electrolyte and counter and reference electrodes immersed into the electrolyte. A potentiostat is connected to the structures and the electrodes and the electrochemical measurements acquired. Once the measurements are completed, the setup must be reversed with the counter and reference electrodes removed and stored, the electrolyte drained and stored or disposed of, the bottomless cylinder removed, and the structure cleaned of any sealant. Examples of this type of apparatus include the Gamry Instruments PTC1 Paint Test Cell, the Princeton Applied Research Tait Cell K0307, and the Princeton Applied Research Flat Cell K0235. The PTC1 Paint Test Cell and the Flat Cell K0235 require the specimen to be clamped to the open end of the container and thus limit the size and configuration of specimens capable to be studied. The Tait Cell holds the specimen via threaded rods and a backing plate. It could be attached to a large structure provided that holes were drilled into the structure—a practice that is rarely allowed. All require a separate (large) potentiostat to be connected to the electrodes and specimen.
An analysis detected a number of documents of interest related to these patents and to the present invention. Table 1 identifies these patents.
TABLE 1Pat.TitleInventorU.S. Pat. No. 7,265,559Self-calibrating corrosion measurement field device withHladky, K. et al.improved signal measurement and excitation circuitryU.S. Pat. No. 7,245,132Intrinsically safe corrosion measurement and history logging fieldPoirier, D. M. etdeviceal.U.S. Pat. No. 7,239,156Configurable corrosion measurement field deviceHladky, K et al.U.S. Pat. No. 7,180,309Electronic system for multielectrode sensors and electrochemicalYang, X. S.devicesU.S. Pat. No. 7,148,706Embeddable corrosion rate meters for remote monitoring ofSrinivasan, R. etstructures susceptible to corrosional.U.S. Pat. No. 7,397,370Monitoring an environment using a RFID assemblyBratkovski, AUS20060144719Quantitative, real time measurements of localized corrosionGill, R. P. et aleventsU.S. Pat. No. 7,034,660Sensor devices for structural health monitoringWatters, D. G. etal.U.S. Pat. No. 6,776,889Corrosion monitoringAtherton, E.U.S. Pat. No. 6,683,463Sensor array for electrochemical corrosion monitoringYang, L. et al.U.S. Pat. No. 6,611,151Coating assessment system based on electrochemical noiseRuedisueli, R. L.et al.U.S. Pat. No. 6,320,395Apparatus and method for electrochemical corrosion monitoringBosch, R.-W etal.U.S. Pat. No. 6,294,074Electrode design for corrosion monitoring using electrochemicalLin, Y. P. J. et al,.noise measurementsU.S. Pat. No. 6,280,603Electrochemical noise technique for corrosionJovancicevic, V.US20050122121Direct Resistance Measurement Corrosion ProbeGilboe, D.
These patents involve a variety of different means to detect corrosion or the corrosivity of the environment, including fiber optic measurements, strain gauges, electrical resistance, electrochemical noise, current between two electrodes, and degradation of witness material. Some are valid only for metal surfaces; others only for painted surfaces. None include a self-contained electrochemical cell that directly measures electrochemical properties of the structure of interest, stores the results, and transfers them to a portable computer or similar device.